This invention relates generally to monolithic series-connected solar cells, and more particularly the invention relates to electrically isolating adjacent cells in such a structure.
The invention is related to the invention in copending application Serial No. 272,105, filed Nov. 14, 1988, for "Solar Cell Having Interdigitated Contacts and Internal Bypass Diodes".
The semiconductor solar cell comprises a plurality of p and n conductivity-type regions in a semiconductor body which generate a voltage potential and/or a current when electron-hole pairs are created in the semiconductor body in response to impinging radiation, and the holes and electrons migrate to the p-doped region and n-doped region, respectively. Because of the small voltage generated in each cell, for example 0.8 volts open circuit for a silicon concentrator cell, cells are serially connected to achieve higher operating voltages. In monolithic structures where the cells share a common substrate, electrical isolation of the cells must be provided.
Heretofore a number of monolithic solar cell configurations have been provided for serially connecting the individual cells. Borden U.S. Patent No. 4,278,431 proposes a mesa structure for each cell with the mesa physically separating epitaxial layer regions which comprise the active portions of each cell. The cells are then serially connected by metal plating formed over oxide isolation in the grooved regions between mesas. Goetzberger U.S. Pat. No. 4,330,680 uses physical shaping to increase electrical resistance of a semiconductor substrate between cells and thereby provide enhanced electrical isolation. P and n regions for each cell are formed on opposing sides of the substrate, and grooves are chemically etched from alternate sides of the substrate to increase resistance of the substrate between cells.
The interdigitated solar cell has p and n regions formed in alternating rows in one surface of a substrate with metal contacts provided contacting all of the doped regions in one row and with all rows of like doped regions being connected in parallel. Electrical isolation between cells in the interdigitated solar cell depends on the resistance of the high-resistivity semiconductor substrate.